System Composition and Detection Principles
The technical architecture of the electrical fire monitoring system is based on continuous monitoring and intelligent analysis of precursor characteristic parameters before electrical fires occur. According to GB 14287 "Electrical Fire Monitoring System" Part 1 (General), the electrical fire monitoring system shall be classified by detection parameters into three basic types: residual current type, temperature-measurement type, and fault arc type. Five-star hotels typically adopt a combined residual current and temperature-measurement scheme, with fault arc detection added in special locations (such as older circuit retrofits). Residual current detection principle: According to Kirchhoff's current law, in a three-phase four-wire power supply system, during normal operation the vector sum of the A, B, C phase currents and the N-line zero-sequence current is zero (IA+IB+IC+IN=0). When insulation damage causes ground leakage, the vector sum is not zero, and the resulting difference is the residual current. The residual current transformer (zero-sequence current transformer) encloses all phase conductors and the neutral conductor of the circuit and detects this differential signal. Setting range: The pre-alarm value is generally set at 300mA (hotel public areas) and 500mA (guest room areas). The operating value is set at 1,000mA–2,000mA (alarm signal emission requires a delay of 0.5–2s to prevent false alarms). Applicable standard: GB 14287.2-2014 "Electrical Fire Monitoring System Part 2: Residual Current Type Electrical Fire Monitoring Detectors." Temperature-measurement detection principle: Temperature sensors (negative temperature coefficient NTC thermistors or thermocouples) directly contact the surface of monitoring points (cable joints, terminal blocks, circuit breaker contacts, etc.) to measure surface temperature. When the temperature exceeds the set threshold, an alarm signal is emitted. Setting range: Pre-alarm value 70–80°C (upper limit of normal cable operating temperature), alarm value 90–105°C (exceeding the maximum allowable operating temperature of 70°C for PVC-insulated cables and 90°C for XLPE). Sensor installation locations: Main switch incoming and outgoing terminals of distribution cabinets/boxes, busbar connections, large-capacity fuse bases, transformer low-voltage side outgoing terminals, etc. Applicable standard: GB 14287.3-2014 "Electrical Fire Monitoring System Part 3: Temperature-Measurement Type Electrical Fire Monitoring Detectors." Fault arc detection principle: Detects the characteristic high-frequency current signals and current waveform distortion features of series arcs (arcs generated at loose connections or broken conductors) and parallel arcs (arcs generated by inter-phase insulation damage) in circuits. By analyzing the flat-shoulder characteristics and frequency components (2–100kHz) of the current waveform, normal arcs (motor brush sparks, switching operations) are distinguished from fault arcs. Suitable for monitoring areas with high arc risk such as older circuits, kitchen equipment circuits, and high-power appliance circuits. Applicable standard: GB 14287.4-2014 "Electrical Fire Monitoring System Part 4: Fault Arc Detectors." System architecture design: The monitoring host (wall-mounted, LCD touch screen) is installed in the fire control room and connects to area detectors on each floor via a two-wire bus (non-polarized, communication distance ≤1,000m) or RS485 bus. The detection host has display, storage, query, printing, and linkage output functions. It is recommended that each host manage ≤256 detectors. The communication protocol shall comply with the communication protocol required by Appendix A of GB 14287.1. The system shall have a self-test function (periodic detection of each detector's operating status and communication line integrity). Power supply requirements: The monitoring host and detectors shall be powered by the fire power supply (connected to a dedicated circuit of the fire alarm system) and equipped with UPS backup power (continuous power supply time ≥30min).
Detector Installation Points and Installation Technical Requirements
Reasonable detector point placement and code-compliant installation are prerequisites for the effectiveness of an electrical fire monitoring system. According to Section 5.3 of GB 14287.2 "Electrical Fire Monitoring System Part 2: Residual Current Operated Electrical Fire Monitoring Detectors" and Section 9.2 of GB 50116 "Code for Design of Automatic Fire Alarm Systems," detector placement shall cover all levels of the building's power distribution system and meet installation spacing and spatial requirements. Placement principles for residual current detectors: (1) Install at the power supply incoming line of distribution cabinets/boxes at all levels of the low-voltage distribution system: substation low-voltage outgoing cabinets (each circuit), floor distribution room main incoming lines (at least 2 per floor), and critical equipment distribution boxes (fire water pumps, sprinkler pumps, smoke exhaust fans, elevators, kitchen main distribution boxes, etc.). (2) In hotel guest room areas, it is recommended to install residual current detectors at the outgoing lines of each floor's distribution box, covering all guest room power supply circuits. (3) Distribution boxes in damp and high-temperature locations such as kitchens, laundries, and boiler rooms must be equipped with residual current detectors (because electrical wiring in these areas is prone to moisture and insulation degradation). (4) In explosion-hazard areas such as diesel generator rooms, boiler rooms, and oil-fired boiler rooms, explosion-proof residual current detectors shall be selected (Ex dⅡBT4 or Ex eⅡT4). Installation requirements for residual current transformers: (1) The transformer shall be installed around all phase conductors and the neutral conductor of the power supply circuit (L1, L2, L3, and N conductors shall all pass through simultaneously; the PE protective earth conductor shall not pass through). (2) The transformer shall be installed close to the circuit breaker outgoing terminal (distance ≤0.5m), mounted vertically (must not be inverted), and secured on the guide rail or bracket within the distribution cabinet/box. (3) Sufficient operating space shall be reserved at the installation location (for ease of removal and maintenance), with a clearance ≥20mm between the transformer and surrounding metal components. (4) The monitored cable shall pass through the center hole of the transformer, with uniform spacing between the cable and the inner wall of the transformer (concentricity deviation ≤10%); otherwise, detection accuracy will be affected. Placement principles for temperature sensors: (1) Install at the incoming and outgoing terminal connections of the main switch within distribution cabinets/boxes (highest heating risk). (2) Install at busbar connections (bolted connection points are prone to loosening and heating). (3) Install at the contacts and wiring terminals of large-capacity circuit breakers (≥400A). (4) Install at cable-to-equipment connections (such as transformer low-voltage outgoing terminals and generator outgoing terminals). (5) Install on cable surfaces at wall penetrations and cable tray bends. Installation requirements for temperature sensors: (1) The sensor shall be directly secured to the surface of the measured point (fixed with metal clips or cable ties to ensure good thermal contact), with a contact area ≥80% of the sensor's temperature-sensing surface. (2) Sensor leads shall use high-temperature-resistant wire (temperature rating ≥150°C) and maintain a clearance ≥100mm from power cables. (3) When multiple temperature sensors are installed in the same distribution cabinet, they shall be clearly numbered and correspond one-to-one with the monitoring host channels. Communication line routing: Detectors and sensors are connected to area controllers and the monitoring host via two-wire bus or RS485 bus. Communication lines shall use shielded twisted-pair cable (RVSP-2×1.5mm²) with a clearance ≥300mm from power cables. Matching resistors (120Ω) shall be installed at the bus ends. Section 9.3.5 of GB 50116 stipulates that communication buses of electrical fire monitoring systems shall use fire-resistant or flame-retardant cables with a protective layer thickness ≥20mm.
System linkage control and alarm handling procedures
The linkage control between the electrical fire monitoring system and the fire alarm system, as well as the effective handling of alarm information, are key to the system's practical effectiveness. According to Section 9.5 of GB 50116 "Code for Design of Automatic Fire Alarm Systems," the electrical fire monitoring system shall operate as an independent subsystem of the fire alarm system, and its alarm signals shall be displayed and recorded in the fire control room. Linkage control methods: (1) Independent operation mode (recommended for five-star hotels): The electrical fire monitoring system operates as an independent system, continuously monitoring and providing early warning for leakage and abnormal temperature parameters of distribution circuits. When anomalies are detected, the monitoring host issues audible and visual alarms (distinct from the fire alarm buzzer), and a dedicated monitoring display screen is set up in the fire control room. Electrical fire monitoring system alarms do not directly trigger power cutoff (to avoid accidental disconnection causing hotel operational interruption); instead, engineering department personnel confirm on site and determine the handling plan. (2) Linkage cutoff mode (only applicable to specific high-risk areas): For high fire-risk areas such as kitchens, laundries, and boiler rooms, non-fire power supply in the area may be automatically cut off simultaneously with the electrical fire alarm (via shunt trip devices or contactors). Power supply circuits for fire equipment such as fire water pumps and smoke exhaust fans are strictly prohibited from automatic cutoff due to electrical fire monitoring system alarms. Alarm tiered management: (1) Early warning value (Level 1 alarm): residual current 300-500mA or temperature 70-80°C. The system issues audible and visual prompts (distinct from fire alarms); duty personnel record and notify the engineering department for investigation. Investigation includes: checking circuit insulation condition, checking whether electrical equipment has leakage, and checking whether cable joints are loose or overheating. After investigation is completed, the alarm is cleared and records are archived. (2) Alarm value (Level 2 alarm): residual current 500-1,000mA or temperature 80-105°C. The system issues audible and visual alarms; duty personnel immediately notify the engineering department supervisor, who arrives on site within 5 minutes for confirmation. After confirmation, handling shall be completed within 30 minutes (cutting off the faulty circuit or replacing damaged components). If timely handling is not possible, a power outage shall be requested to ensure safety. (3) Severe alarm (Level 3 alarm): residual current >1,000mA or temperature >105°C. The system issues a strong alarm (similar to the fire alarm sound); duty personnel handle it according to fire alarm procedures: immediately notify the engineering department director and security department, cut off power supply to the faulty circuit (via shunt trip device), evacuate surrounding personnel, and prepare fire extinguishing equipment. Alarm record management: All alarm events (including early warnings, alarms, and false alarms) shall be recorded in the system log, including: alarm time, alarm type (residual current/temperature/arc), alarm value, circuit number, location description, handling personnel, handling result, and alarm clearance time. Records shall be retained for ≥3 years (required by Section 9.5.5 of GB 50116). A monthly alarm statistical analysis report shall be generated to identify high-frequency alarm circuits and areas, analyze root causes, and implement improvement measures. Marriott MIDS standards require that the response time for electrical fire monitoring system alarms (from alarm to on-site confirmation) shall not exceed 10 minutes (Level 1 alarm) and 5 minutes (Level 2 alarm).
System maintenance and periodic testing requirements
The maintenance and periodic testing of the electrical fire monitoring system are necessary management measures to ensure long-term stable operation of the system and to avoid equipment aging and rising false alarm rates. According to Chapter 6 of GB 14287.1 "Electrical Fire Monitoring System - Part 1: Electrical Fire Monitoring Equipment" and Section 9.6 of GB 50116 "Code for Design of Automatic Fire Alarm Systems," the electrical fire monitoring system should establish a complete maintenance management system and periodic testing plan. Routine maintenance (daily/weekly): (1) Daily inspection: fire control room duty personnel check the operating status of the monitoring host (power indicator, communication indicator, and display normal). Confirm through the host self-test function that all detectors are online and normal (equipment online rate should be 100%). (2) Weekly inspection: retrieve historical data from the past week and check for low-frequency warning events (small leakage currents or slight temperature rises that may be overlooked). Analyze the daily variation trend curve of residual current to identify abnormal fluctuations (e.g., the residual current of a loop gradually rising from 50mA to 150mA, indicating continuous insulation deterioration). Periodic testing (monthly/quarterly/annual): (1) Monthly functional test: manually test the alarm function of each detector (by issuing detector self-test commands through the host) to verify normal audible and visual alarms. Testing should be conducted during non-operating hours (e.g., 2:00-5:00 a.m.) so as not to affect the guest experience. Test records shall form a monthly report. (2) Quarterly testing: select no less than 30% of residual current transformers for actual measurement and calibration (using a standard leakage current generator with three calibration levels of 100mA, 300mA, and 500mA output); deviation should be within ±5%. Select no less than 20% of temperature sensors for actual measurement comparison (using a standard temperature source or precision thermometer for comparison); deviation should be within ±3°C. (3) Annual comprehensive testing: perform functional testing and accuracy calibration on all detectors (including residual current transformers and temperature sensors). Check the insulation resistance of communication lines (≥20MΩ). Test the linkage function between the monitoring host and the fire alarm system (simulate an alarm signal transmitted to the fire alarm system). Issue an annual testing report after comprehensive testing. Equipment replacement and life management: (1) The service life of residual current transformers is about 10-15 years; they should be replaced when the leakage detection value deviation exceeds ±10% or the internal coil is open-circuited. (2) The service life of temperature sensors (NTC thermistors) is about 5-8 years; they should be replaced when the detection value deviation exceeds ±5°C or the response becomes slow (thermal time constant exceeding the specified value). (3) The UPS battery of the monitoring host should be replaced every 3-5 years (lead-acid battery) or 8-10 years (lithium battery). Spare parts management: it is recommended that the hotel keep a spare parts inventory of at least 10% of key components (transformers, sensors, communication modules). Service contract: it is recommended to sign an annual maintenance service contract with the system supplier (including software upgrades and hardware maintenance). Clause 9.6.3 of GB 50116 requires that the maintenance and testing of the electrical fire monitoring system be performed by qualified units or personnel, and testing records shall be archived for reference.